1. Field of the Invention
The present invention relates to a control system for an engine of an automobile and, more particularly, to an automobile engine control system in which the amount of intake air to be introduced into an engine at the end of an intake stroke is predicted based on a factual amount of intake air introduced into the engine prior to the end of the intake stroke.
2. Description of Related Art
Typically, automobile engines of a fuel injection type have air-flow sensors for detecting the amount of intake air introduced into the engine. An engine control system calculates an air charging efficiency based on the factual amount of intake air and, after having determined and corrected a basic required amount of fuel according to the air charging efficiency, provides a control signal so as to inject the corrected amount of fuel into the engine.
In a case in which the engine control system determines the air charging efficiency based on the factual amount of intake air detected by, for instance, an air-flow sensor at the end of an air intake stroke, it is too late for the calculation of a required amount of fuel and, hence, injection of the required amount of fuel. Accordingly, it is essential to determine an air charging efficiency based on the factual amount of intake air detected prior to the end of an air intake stroke. While this does not provide any problems for engine operation under ordinary driving conditions, nevertheless, because changes in the amount of intake air may possibly occur at the end of an air intake stroke after detection of the intake air amount under transitional driving conditions, such as acceleration and deceleration, it is regarded that the detection of intake air amount is not always adequate and accurate.
In order to avoid such an inadequate detection, it has been proposed to estimate or predict a required amount of intake air to be introduced at the end of an intake stroke based on a change in the factual amount of intake air detected by an air-flow sensor prior to the end of the intake stroke and determine engine control parameters according to the required amount of intake air. Such an automobile engine control system is known from, for instance, Japanese Unexamined Patent Publication No.63-8296.
However, the engine control system described in the above publication has a problem in that the air-flow sensor is exposed to pulsation of intake air which is caused due to intermittent introduction of intake air into cylinders. Because a "hot-wire" type of air-flow sensor is very sensitive to such pulsation, an output of the air-flow sensor often reflects the pulsation of intake air on the required amount of intake air. This is more remarkable when the required amount of intake air is estimated by multiplying the sensor output by an estimate coefficient, leading to an inaccurate required amount of intake air. An inaccurate required amount of intake air results in an error in fuel injection and, as a result, a large change in air-fuel ratio, so as to provide a deterioration in emission control. This is because the pulsation of intake air is apparently amplified by the estimate coefficient.